1. Field of the Invention
The invention relates to a shell structure for living tissue replacement, particularly replacement of segments of long bones.
2. Description of the Prior Art
Large bone defects may be caused by severe trauma, by treatment complications (infection), or by the removal of bone tumors. There are several methods currently used for treatment of such defects. The methods of bone segment transport--as developed by ILIZAROV--produce new bone by distracting a zone of tissue growth. This works very well for diaphyseal defects, where the bone geometry is simple and generally cylindrical. The treatment lasts rather long (1 mm per day plus consolidation time of several weeks to several months) and requires an external frame.
Another method is to replace the defect with an artificial permanent implant, i.e. a prosthesis. These prosthesis are made from metals, plastics, ceramics or combinations of these. They serve the purpose of structural support, but usually lead to long term complications. With improved treatments of bone tumors, patients, life expectancy is likely to exceed life expectancy of currently used prosthesis. Another method used for treatment of large defects, especially those involving complex anatomical structures such as joints, is transplantation. Similar to blood banks, bone banks exist to provide a supply of bones for allografts. Typically, the transplant is dead and is never revitalized passed a short distance from the interface to the host tissue. Long term success of the transplants is very low.
Autografting of bone defects with cancellous bone material is the most widely used technique. The availability of the material is limited and the current practice is extremely inefficient in using the graft. Typically the grafting bone is crushed into small pieces (collected mainly from pelvic bone) and laid into the defect. In a major bone the volume of the defect is large and the graft is initially without a viable vascular supply. Large volumes cannot be supported by nutrients from the surrounding tissue and most of the graft cells die leading to a large volume of necrotic tissue which presents a major burden to the immune system. These grafts have at best been contained to their intended location by wrapping into either appropriate natural tissues or artificial membranes.
All these methods have failed in producing predictable replacement of living tissue and are only partially satisfying.